STS-67 Day 10 Highlights

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On Sunday, March 12, 1995 at 9:30 a.m. CST, STS-67 MCC Status Report # 20 reports: Tammy Jernigan, Sam Durrance and Wendy Lawrence assisted ground controllers in Alabama with fine-pointing of the three telescopes. For the first time, an observation was made of the Moon as the Shuttle passed south of Hawaii on the 161st orbit of the mission in an effort to gather ultraviolet data to help determine the Moon's origin. Several additional observations of moons and asteroids will be made throughout the mission.

On Sunday, March 12, 1995 at 6 a.m. CST, STS-67 Payload Status Report # 21 reports: (10/5:22 MET) Mission Specialist Wendy Lawrence maneuvered the orbiter into the required position, while Payload Commander Tammy Jernigan aligned the Instrument Pointing System (IPS) at the most difficult-to-acquire Astro-2 target, our moon. Payload Specialist Sam Durrance coordinated with science teams at Marshall Space Flight Center in Huntsville, Ala., to accurately point the Ultraviolet Imaging Telescope (UIT) at the moon. "The entire moon has never been imaged in the ultraviolet wavelengths, and we're looking forward to seeing these data," said UIT Guest Investigator Dr. Chan Na of Southwest Research Institute. No similar data have been obtained from either previous Shuttle missions, the Apollo program or Clementine, and there are no operating or planned spacecraft capable of imaging the whole moon at far ultraviolet wavelengths.

UIT Guest Investigator Dr. Randy Gladstone, also of Southwest Research Institute, is using UIT to make far ultraviolet maps in order to learn more about the surface properties of the moon. "This lunar observation yielded 12 good, wide-field exposures of the moon," said Gladstone. The 70mm UIT film will developed and analyzed when Endeavour returns to Earth. UIT data gathered during Astro-2 will be used to test the hypothesis that the far ultraviolet surface brightness of an object without an atmosphere is a good indicator of the length of time that the surface has been exposed to space. These data will also help scientists understand future ultraviolet images of asteroids and other planetary satellites.

The Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE) telescope observed the moon along with UIT last night to determine how well the WUPPE instrument could detect such features as dark seas or bright craters on the moon. Video from the WUPPE guide camera showed the instrument could clearly distinguish these lunar surface features. WUPPE scientists will now decide what observational goals they will set for the next lunar observation, later in the mission.

Durrance also pointed the WUPPE telescope to a cool, giant star known as Alpha Orionis. This star, which pulsates about every five years, is approximately 14,000 times as radiant as our sun. WUPPE Principal Investigator Dr. Arthur Code will analyze the data from this Astro-2 observation to learn more about what effect these pulsations have on the envelope of gas and dust surrounding Alpha Orionis.

Pilot William Gregory moved Endeavour into position, Mission Specialist John Grunsfeld aligned the IPS and Payload Specialist Ronald Parise again pointed the Hopkins Ultraviolet Telescope (HUT) at the quasar known as 1700+64. This quasar is the most distant object the HUT team is observing during Astro-2. HUT Principal Investigator Dr. Arthur Davidsen, of Johns Hopkins University, is using the quasar to provide background lighting in a search for helium in the intergalactic medium (the gas between galaxies). Helium is thought to be left over from the "Big Bang," a primordial fireball that many astronomers believe marked the birth of the universe about 10 to 20 billion years ago.

The HUT telescope also observed a portion of the Cygnus Loop, a "middle-aged" supernova remnant, over night. Supernova remnants are visible evidence of the final cycle of stellar evolution and important sources of information for astronomers. The Cygnus Loop is of particular interest because it reveals details about the structure and velocity of shock waves from the explosion of a dying star) as they travel through the interstellar medium. HUT's spectrographic data will help scientists determine temperatures, densities and chemical compositions of the gases located in the Cygnus Loop.

HUT team members say their recent observations of the Vela supernova remnant will allow scientists, for the first time, to measure the same supernova remnant shockwave from two angles. The Vela observations seem to show the same filament of expanding gas from the stellar explosion both edge on and face on. "If we can compare this filament in two positions, and verify that the models work for this object, we can generalize that and compare it to other data we've taken on the Cygnus Loop, the Vela supernova remnant and with other telescopes," said HUT Co-investigator Dr. Bill Blair. If successful, the comparison should give researchers a much better understanding of supernova remnants.

Parise pointed WUPPE and HUT at a hot, massive star called 48 Librae, located in the constellation Libra. This star spins rapidly and has an outer layer that shows evidence of being peeled off by stellar winds. Previous observations of this star have suggested that its stellar winds are strongest near the star's equator because of its rapid rotation. WUPPE scientists are examining the polarization of this star's light to learn more about the scattering by electrons in the disk surrounding it. HUT scientists are trying to determine an accurate temperature for this star, search for stellar winds, and study absorption in the gas and dust between this star and nearby stellar objects.

Jernigan and Durrance aligned WUPPE and HUT to look at a supergiant star, P Cygni. This star, which increases in brightness like a nova, has remained just visible to the naked eye for more than 100 years. Scientists believe it is not a true nova, rather a variable star surrounded by an expanding gaseous shell. WUPPE scientists are interested in P Cygni because it is ejecting mass at a colossal rate. As P Cygni scatters light, it produces a pronounced polarization which differs from theoretical models. Data from these Astro-2 observations will test refined theories and offer greater insight into the mysterious variability of P Cygni.

Throughout the next 12 hours, HUT, WUPPE and UIT will be used to observe the planet Mars, look at young stellar populations in galaxies, examine supernova remnants and study a reflection nebula in a dark cloud.

On Sunday, March 12, 1995 at 5 p.m. CST, STS-67 MCC Status Report # 21 reports: Both Grunsfeld and Parise enjoyed a few hours off to relax before heading into the final days of the mission, trading places on the aft flight deck to operate the Instrument Pointing System and the telescopes while the other took a break from research duties. Gregory used Endeavour's ham radio gear to talk to students at the J.J. Fray Elementary School in Rustburg, Virginia and the crew continued to respond to questions about their mission and spaceflight in general placed on the Internet and faxed up to the Shuttle by flight controllers.

On Sunday, March 12, 1995 at 6 p.m. CST, STS-67 Payload Status Report # 22 reports: (10/17:22 MET) The Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE) team selected Nova Circinus 1995 for observation this morning. This is the third "new" nova -- a binary star system whose first outburst was observed very recently -- to be studied by the Astro-2 telescopes. "Though all three novae went into outburst since the first of the year, each is at a different stage in its history," said WUPPE Principal Investigator Dr. Arthur Code. "By comparing their polarization, we hope to determine whether gas from novae outbursts is expelled in a spherical shape and then becomes more asymmetrical, and if so, how quickly the asymmetry develops." Light is polarized when it encounters an asymmetrically shaped object, such as a flattened gas disk, which causes the light to vibrate in preferred directions.

"Every day brings new surprises," said HUT Co-investigator Dr. Bill Blair, describing the success today of two supernova remnant observations he admits were long-shots. HUT led a study of the supernova remnant Puppis A, the third supernova remnant Astro-2 has observed in our Milky Way galaxy. HUT and WUPPE examined a filament of gas in the remnant's eastern region, apparently an interaction between an interstellar cloud and the blast wave speeding from the supernova explosion. "The International Ultraviolet Explorer barely detected this remnant, so we didn't know what to expect," said Blair. "We thought dust in the interstellar medium might block its ultraviolet radiation, but we got a very nice spectrum which showed strong nitrogen emissions." Blair said it is possible the nitrogen could have been thrown out by the massive star thousands of years before it exploded as a supernova, and now the shock wave from the blast is catching up with nitrogen expelled from the star.

Supernova 1006, whose explosion in A.D. 1006 makes it a relatively recent supernova, provided another first. "The shock wave from this supernova is moving very fast, plowing through interstellar space at about 2,000 kilometers (1,250 miles) per second, as opposed to 150 to 200 kilometers per second in remnants like Puppis A," said Blair. "We thought its emissions might be too faint for us to observe, but we felt it was important enough to attempt. This gives us a new range of velocity that has never been observed before in the ultraviolet." Blair said the HUT spectrum may show the primary passage of the supernova blast wave as it first encounters interstellar gas. Comparison with optical observations could help astronomers understand the basic physics of supernova shock fronts.

The Ultraviolet Imaging Telescope team led eight highly successful observations in a row. UIT captured the mission's first images of the Whirlpool Galaxy (M 51) for Dr. Wendy Freedman's atlas of spiral galaxies. The Whirlpool Galaxy is the larger of two interacting galaxies close enough together to disturb each other through gravitational force. M 51 is a large spiral galaxy with a mass 100 billion times that of our sun. It is interacting with NGC 5195, a much less massive galaxy. Astronomers will study UIT photographs to learn more about the formation of stars in that system, especially in the bridge of matter that joins the two interacting galaxies.

UIT also imaged CB_4, a cold cloud of interstellar gas and dust which is sufficiently dense to obscure starlight from objects behind it, while it reflects light from objects in front of it. Though this so-called dark cloud is relatively faint, Astro scientists were able to obtain measurements to test models of dust in the interstellar medium during a daylight observation.

The imaging telescope also photographed a cluster of galaxies known as the Coma Cluster. UIT is examining the dense cluster, made up primarily of elliptical galaxies, to obtain simultaneous information on large samples of galaxies. Astronomers will study the integrated ultraviolet properties of these large samples to determine constraints on the physics of cooling flows, as hot gas may condense into stars as it rains down on a galaxy from the intra-cluster medium. Scientists also will look for the presence of dark matter, which does not emit appreciable radiation.

HUT and WUPPE observed NGC 4874, the central elliptical galaxy in the Coma Cluster, to determine the ages of its stars. Though elliptical galaxies have comparatively few young stars, they emit more ultraviolet radiation than would be expected from a population of old stars. Astro-1 observations of ellipticals suggest this radiation may come from aging stars in a previously unknown stage of evolution. Astro-2 is following up on the mystery.

UIT photographed the open star cluster NGC 7789, and investigations into new star formation included observations of elliptical galaxy NGC 185, irregular galaxy NGC 1313 and rapid star formation galaxy NGC 4631. WUPPE led the mission's first observation of the Planet Mars, and it observed interstellar polarization probe HD 217490 to add to its ongoing study of the dust scattered throughout our Milky Way. Dr. Brian Espey got excellent HUT and WUPPE data on the symbiotic star system RR Telescopii for his study of closely orbiting stars with radically different temperatures.

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